1. Field of the Invention
The invention relates to an industrial belt and more particularly relates to a paster belt that carries battery paste for use in the manufacture of lead-acid batteries and the method of its fabrication.
2. Description of the Prior Art
The present invention relates to an industrial belt, particularly a battery paster belt that is used in the manufacture of lead acid batteries. The conventional lead-acid batteries consist of several positive and negative plates separated by porous separators. The plates are produced by pasting a lead oxide material over a lead wire grid. After the positive and negative plates are pasted, they are cured, with each of the plates having a lug disposed on the top portion of the plate. Prior to these plates being placed in the battery container, a separator is placed between each plate and the negative and positive plate lugs are joined by two separate plate straps, one for the positive plate lugs and one for the negative plate lugs. Once placed into the container the intercell connections are made and the battery container and cover are sealed together. The battery is electrochemically formed by welding the positive and negative posts in the cover, and adding the acid.
There are many known processes for making lead-acid batteries. In brief, the process involves feeding a ribbon of lead into an inline expander to produce a continuous bilateral length of grid making stock. The stock has a central unexpanded strip and two unexpanded strips at the lateral edges. Between the central unexpanded strip and each lateral edge, there is a network of grid wires formed by the expander. The grid-making stock enters a belt paster for filling the grid network with battery paste. The pasting machine sandwiches the grid making stock and paste between paper strips fed from paper rolls. Plate forming stock exits the paster and passes into an oven for drying. Following drying and cutting, the plate forming stock is ready for curing. After curing, a stacker accumulates the plates for subsequent processing into a lead-acid battery.
During this process, the battery plates are normally produced by passing cast grids through an orifice-type or belt-type paster. Plates may be “flush pasted” (i.e., the thickness of the paste layer is approximately equal to the thickness of the grid) or “overpasted” on one side (i.e., the paste layer is flush with one surface of the grid but extends beyond the surface of the grid on the opposite side). In either case, the surfaces of the paste on opposite sides of the plate are normally smooth and parallel.
State of the art paster belts include 6-8 ply integrally woven layer cotton belts which are glued/sewn to make endless felts such as that described in U.S. Pat. No. 4,604,310. There are several drawbacks to these type of belts. Such belts typically have poor dimensional stability, in which the belts can elongate when wet and can exceed the maximum machine take-up on the most common paster machines due to a creep greater than 1.5% within usually 24 hours after installation. Also, the seam construction in cotton belts typically involves manually gluing and sewing for the required strength during operation. This manual process results in seams with wide strength variability, and accordingly a poor belt product consistency. Seam failure is a significant problem for such belts in operation. Additionally, in the seam area, which is typically about 3 inches long in the machine direction (“MD”), there is an impermeable zone which creates one off-spec battery plate with each revolution.
The dimensional stability of the aforementioned belt is obtained by use of many wrapped layers of high modulus polyester (PET) multifilament yarns. However, these many layers of fine fabric are easily damaged during the subsequent needling operation to add one or more batt fiber layers, which results in a wide distribution of creep characteristics in operation from belt to belt. Also, in paster belts it is desired that it imparts a certain type of mark in pasted plates to improve the surface area which provides for more cold cranking amps in the final battery product. To impart this mark, the surface of the paster belt must have a durable textured surface which can provide a consistent mark throughout the usable life of the belt.
However, the belts currently used employ threads of cotton and/or synthetic spun fibers (polyester or polyamide) in a plied structure for both wicking and texture. These threads are easily deformed and flattened by the 0.68-2.068 Mpa pressure that is exerted onto the belt under the pasting hopper causing a great reduction in surface texture as a function of time. This reduction in texture not only causes reduced plate surface area, but also creates worn grooves in the belt surface at the width of the plates being produced. These grooves prevent the manufacturer from switching between plate widths without installing a new belt as the grooves will result in paste thickness beyond normal specification limits across the belt width.
Also, the typical use of hydrophilic cotton fibers at the surface, which absorb water into their structures, creates an issue with lead oxide adhesion and absorption. This results in belts which tend to harden over time, reducing their water handling capacity, and accordingly adversely affects the belt's pasting efficiency. Moreover, as the lead becomes deeply embedded in the cotton fiber structure, it is difficult or impossible to clean the belt, especially if it is not kept continuously wet.
The present invention is directed to a battery paster belt and a method for forming such a paster belt that overcomes the shortcomings of the prior art.